1. Field of the Invention
The present invention relates to a storage system, and in particular to copying of data among plural storage systems.
2. Description of the Related Art
In recent years, a technique has grown in importance in which, in order to allow a data processing system to provide services even if a failure has occurred in a storage system used for providing continuous services to customers (hereinafter referred to as first storage system), other storage systems (a storage system a relatively short distance apart from the first storage system is referred to as a second storage system, and a storage system a longer distance apart from the second storage system is referred to as a third storage system) are set separately from the first storage system, and copies of data in the first storage system are stored in the other storage systems. As a technique for copying information stored in the first storage system to the second and the third storage systems, there are techniques disclosed in U.S. Pat. No. 6,209,002 and JP-A-2003-122509.
U.S. Pat. No. 6,209,002 discloses a technique in which the second storage system has two copied data corresponding to copy object data in the first storage system, and the third storage system holds one of the copied data.
JP-A-2003-122509 discloses a technique in which the second storage system has only one copied data corresponding to copy object data in the first storage system, and the third storage system can obtain the copied data without requiring a redundant logical volume for carrying out remote copy as described in U.S. Pat. No. 6,209,002.
As described above, in the conventional techniques, the second storage system is provided between the first storage system and the third storage system, which is located a long distance apart from the first storage system, to realize long-distance remote copy while preventing data loss such that a copy of data in the first storage system is obtained in the third storage system.
However, some users may require a remote copy system in which cost for system operation is considered while failure resistance of data is increased through long-distance copying. For example, a copy of data in the first storage system only has to be held in a storage system located a long distance apart from the first storage system.
In order to give a complete copy of data in the first storage system to the third storage system, which is located a long distance apart from the first storage system, in preparation for a failure, when influence on performance of the first storage system is taken into account, it is necessary to arrange the second storage system between the first storage system and the third storage system and transfer the data from the first storage system to the third storage system through this second storage system. In such a case, it is desired to minimize a logical volume that is used in the second storage system as much as possible.
However, in the case in which it is attempted to remotely copy data from the second storage system to the third storage system located a long distance apart from the second storage system, the second storage system is required to have a volume (copied volume) that is the same as a volume of the first storage system. This volume increases as a capacity of the volume of the first storage system increases.
It is needless to mention that, even if the technique disclosed in JP-A-2003-122509 is applied, the second storage system inevitably has a volume with the same capacity as the copy object volume in the first storage system.